Process for reducing the grain in precious metals and their respective alloys



atented Jan. 10, 1939 PROCESS FOR REDUCING THE GRAIN IN PRECIOUS METALS AND THEIR RESPEC- TIVE ALLOYS Wilhelm Truthe, Frankfort-on-the-Main, Germany, assignor to Deutsche Gold and Silber Scheideanstalt vormals Roessler, Frankforton-the-Main, Germany, a corporation of Germany No Drawing. Application February 12, 1938, Se,-

rial No. 190,331. 1937 In Germany February 22,

6 Claims. '(Cl. 75135) My invention relates to a process for reducing the grain in precious metals and their respective alloys and refers in particular to the manner in which the grain reducing metal is introduced.

It has generally been known that in precious metals like silver, gold, palladium, platinum and the like the presence of little quantities of metals like iridium, rhodium, ruthenium and the like considerably improves the texture of crystals preferably in respect to reducing the size of the grain in the metal or alloy respectively. 1

Different methods have been applied heretofore to incorporate the metals favoring grain reducing. For instance preliminary alloys with platinum made in a preparatory step were used. These preparatory alloys subsequently are called pre-alloy's in the description as well as in the claims. This method proved to be very inconvenient, firstly because rather high temperatures for melting such pre-alloys had to be utilized, as in making up a platinum-iridium alloy 2000 C.

are necessary, and secondly because dissolving the platinum pre-alloy in the molten precious metal respectively in their alloys was considerably time-consuming when ordinary temperatures between 900-1200 C. were applied for melting down the alloys. Even after several hours it was not safe to say that in this case dissolving was complete. When casting the alloy it is of considerable disadvantage when the dissolving has taken place at higher temperatures since large pipes are formed and the cooling alloy solidifies in a coarse-crystalline structure. This is just the opposite of what has been aimed at by the addition of grain reducing metals. In these pre-alloys the small quantity of metals also which cause grain reducing is of considerable disadvantage; for instance, when platinum-iridium alloys containing about 20% of iridium are used, considerably large quantities of platinum have to be incorporated to the precious metal or their respective alloy; this is not always desirable.

It has also been tried to add the grain reducing metals to the fusion in the form of suitable compounds, such asfor instance alkali metal or ammonia double salts. Since relatively small quantities are used which come into contact with the highly heated fusion cause squirting and scatter ing, there is no possibility of guaranteeing the actual content of grain reducing metals in the to .3% in the shape of pre-alloys with non-noble fusion.

According to my invention the metal or metals which cause grain reduction are added in the form of pre alloys which contain non-precious metals. Advantageously I use such pre-alloys which have as high a content of iridium, rhodium or the like as possible; as for the non-precious metals I use, for instance, tin, zinc, cadmium, arsenic, bismuthum and the like.

With special advantage pre-alloys are used which contain iridium as grain reducing metal and tin as the non-preciousmetal, the proportion corresponding advantageously to the formula IrSnz. Such a pre-alloy may be fused at a comparatively low temperature and because of its low melting point it is easily incorporated in the melt distributed therein and dissolved. The tin-iridium alloy can be made after the fashion already known by dissolving iridium in a five to sixteen timeslarger quantity of tin at 1000 C. and after having cooled the resulting productby treating it with hydrochloric acid to get rid of the excessive tin. Only quite small quantities, for instance 0.0020.6%, of the tin-iridium alloys of the formula IrSnz which contain approximately 50% iridium are needed in order to obtain the grain reducing results desired. Consequently only very insignificant and harmless quantities of nonprecious metals are introduced into the melt concerned.

In a similar way I can use other pre-alloys of the grain reducing metals with non-precious metals than those I have described above in accordance to my invention. In this case similarly only very small quantities are required. I have found that one generally can work to the point that the final alloys of precious metals contain only 0.001 to 0.3% of grain reducing metals.

The process has proved to be extraordinarily suitable for reducing the grain of palladium alloys, for instance, those which besides palladium contain silver and copper and as the case may be further ingredients,v as, for instance, gold and/or non-precious metals like nickel and/or zinc. Such alloys can be successfully treated with quantities of 0.01-0.1% of a tin-iridium alloy corresponding to the formula IrSn This process has turned out to be especially useful for reducing the grain of alloys, which serve as dental alloys, for instance, for orthodontal purposes.

vWhat I claim is:

1. The process for reducing the grain in noble metals and thei'r alloys which consists in incorporating metals of the group iridium, rhodium and ruthenium in quantities ranging from .001%

metals.

2. In the process for reducing the grain of noble metals and their alloys by incorporation of iridium which reduces the' grain the step which consists in adding a tin-iridium alloy to melts of such metals and their alloys in sufllcient quantitles that the final product contains substantially .001% to .3% of iridium.

3. In the process for'reducing the grain of noble metals and their alloys by incorporation of iridium the step which'consists in introducing a tin-iridium alloy of the approximate formula IrSnz into a melt of such metals and their alloys in sufllcient quantities that the final product contains substantially .001% to .3% of iridium.

4. In the process for reducing the grain of a silver-palladium alloy by incorporation of iridium the step which consists in introducing a. tiniridium alloy of the approximate formula IrSnz into a melt of such silver-palladium alloy in suflicient quantities that the final product contains substantially .001% to .3% of iridium.

5. In a process for reducing the grain of noble metals and their alloys by incorporation of metals which reduce the grain, the step which consists-in incorporating .002% to .6% of an alloy consisting substantially of 50% iridium and 50% tin with such metals and their alloys.

6. In a process for reducing the grain of noble metals and their alloys by incorporation of metals which reduce the grain, the step which consists in incorporating .01% to .1% of a tiniridium alloy of the approximate formula IrSnz with such metals and their alloys. I

WILHELM TRUTHE. 

